Absorption refrigeration apparatus and method



N. E. HOPKINS 3,254,499

ABSORPTION REFRIGERATION APPARATUS AND METHOD June 7, 1966 Filed Sept.10, 1964 United States Patent 3,254,499 ABSORPTION REFRIGERATIONAPPARATUS AND METHOD Neil E. Hopkins, Spring Garden Township, YorkCounty, Pa., assignor to Borg-Warner Corporation, Chicago, Ill., acorporation of Illinois Filed Sept. 10, 1964, Ser. No. 395,443 3 Claims.(Cl. 62-404) This invention relates to an improved control system forcontinuous cycle, absorption refrigeration apparatus, and moreparticularly to a method and apparatus for minimizing contamination ofthe refrigerant due to explosive flashing and violent boiling in thegenerator. In a conventional absorption refrigeration system, forexample the type which utilizes a hygroscopic brine as the absorbent, aslow load operation, or at system startup, the solution throughout thesystem is more dilute than it is during full load operation. Since theincrease in water content in the solution lowers the boiling point ofthe solution, the generator becomes more vulnerable from the standpointof possible violent boiling action. This condition would be mostaggravated at a condition of low salt concentration, such as exists atlow load, or system open position; The violence of the action at thiscondition can be much greater than that which exists at full 100% plantcapacity, at which conditions the concentration of solution bothentering and leaving the generator are considerably higher. Variousdevices, such as eliminators and baflies, are used to prevent solutioncarryover from the generator to the condenser. It is relatively easy toapply such devices to prevent slopover of this nature during full loadoperation. However, under the conditions discussed above, boiling actioncan be so violent that eliminators and baflles are unable to completelyprevent slopover. This condition can cause the solution to be carriedwith the refrigerant into the condenser and the resulting contaminationof the refrigerant by the lithium bromide solution reduces therefrigeration capacity.

The present invention takes preventative action when .low concentrationsprevail by raising the condensing water temperature supplied to theabsorption system. This raises the condensing water temperature to thecondenser in the top shell, and thus raises the condensing temperatureand pressure. This increased pressure reduces the violence of boiling,such that even with low concentrations and a condition which causes thesteam valve to open wide on a sudden demand for additional cooling,solution carry-over is virtually eliminated.

At full load, the condensing .water temperature isreturned to itsinitial design point. Thus this invention brings about a change incondensing water temperature control to the absorption system, varyingfrom a design condensing water temperature at 100% design load, to asomewhat higher condensing water temperature at a lower load.

In order to achieve this control in a practical manner, the controlsystem must take advantage of certain relationships between solutionconcentration and temperature. For example, the temperature of solutionleaving the generator is related to the concentration of solutionleaving the generator, and also in a general way it is related to theconcentration of the solution entering the generator. By usingtemperature responsive controls instead of means to sense the solutionconcentration, it is possible to-simplify the control system andincorporate it into a conventional absorption system at reasonablecos-t.

In brief, the absorption refrigeration system of the present inventionvaries the condensing water temperature to the absorption system as theload varies. For a given "ice load, the cooling water temperature ismaintained at a fixed condition by a submaster control with atemperature sensitive bulb in the cooling water line for the absorberand condenser. As the system capacity varies, corresponding to a changein the solution concentration and consequently a change in thetemperature from the generator, the control temperature of the submasterinstrument is reset. This action is gradual because of the flywheeletfect of the solution concentration change, and consequently, a slowrate of change takes place in solution temperature.

At the maximum load it is necessary that the condensing watertemperature be at the minimum design setting (usually F.) in order toobtain full equipment capacity. At low load, corresponding to areduction in concentration throughout the system, it is desired to raisethe condensing temperature in the top shell to reduce boiling potentialon a later demand for increased cooling.

In summation then, the control system utilizes a first temperaturecontrol means for maintaining the cooling water in the circuit at theproper temperature. This control means, in a preferred embodiment, isoperative to selectively divert the cooling water through a coolingtower or through a conduit which bypasses the cooling tower. In additionto this temperature control, which is more or less conventional inabsorption systems, the present invention also includes a second(master) temperature controller which is responsive to the temperatureof the solution leaving the generator to vary the control point of thefirst temperature controller, which for the purpose of this invention isa type capable of resetting subm aster) It is therefore a principalobject of the present invention to provide an improved control systemfor an absorption refrigeration apparatus in order to reduce the boilingactivity within the generator and avoid contamination of refrigerant inthe condenser.

Additional objectsand advantages will be apparent from a reading of thefollowing detailed description taken in conjunction with the drawingwherein:

The figure is a diagrammatic representation of an absorptionrefrigeration system embodying the principles of the present invention.

For the purpose of this specification, it will be assumed that theabsorption refrigeration system described herein is of the type whichemploys a hygroscopic brine as the absorbent and water as therefrigerant. Inasmuch as lithium bromide solution has been found to be asuitable absorbing medium, reference will sometimes be made to a systememploying this salt as the absorbent, but it should be understood thatthe invention has general application to absorption refrigerationsystems using any of several other known absorbent-refrigerants. Alsofor purposes of illustration, the concentrated solution means a solutionof relatively higher concentration in lithium bromide (approximately64.5 percent at maximum capacity), while the dilute solution may bedefined as a solution relatively lower in concentration .of lithiumbromide (approximately 59.5 percent at maximum capacity).

Turning now to the figure, a first shell 10 is provided 'having aheat-exchanger 11 and a heat-exchanger 12 disposed therein. A pan orreceptacle 13 positioned below heat-exchanger 12 combinestherewith toform a condenser 14, and heat-exchanger 11 cooperates with the shell 16to form a generator 15.

A second shell 16, ordinarily positioned below shell 10, includes a pairof heat-exchangers 17 and 18. Heat-exchanger 17 is provided with a pan19 which cooperates therewith to form an evaporator 20 andheat-exchanger 18 cooperates with.the lower portion of shell 16 toprovide an absorber 21. A pressure differential exists between shells 10and 16 corresponding to the condenser 3,2 3 pressure and evaporatorpressure of the refrigerant (water).

The absorber has a pump 28 associated therewith for continuouslycirculating solution from sump 26 through conduits 29 and 30 to a sprayheader 31 located above heat-exchanger 18. The concentrated solutionfrom the generator mixes with the more dilute solution in sump 26 toform an intermediate strength solution. Alternatively, the concentratedsolution supply line 25 may be connected directly to line 29. In anycase, the capacity of the absorber pump 28 is greatly in excess of theflow of concentrated solution from the generator so that all of theconcentrated solution from the generator plus considerable quantity ofdilute solution from the absorber is supplied to spray header 31.

A hot concentrated solution line 23 leads from the lower portion ofgenerator-condenser shell 10 to the heat-exchanger 22. In order toincrease the efiiciency of the system, it has been found to be desirableto provide a heat-exchanger 22 to transfer heat from the hot solutionleaving the generator to the relatively cool dilute solution from theabsorber. A concentrated solution line 25 leads from the heat-exchanger22 to a dilute solution sump 26 (shown partially broken away toillustrate a separate sump 26) provided in the lower portion of shell16.

A dilute solution line 32 connects the generator pump 33 to a secondsump 26', referred to above, which is spaced longitudinally of the shell16 from sump 26 and entirely separate therefrom. The cool dilutesolution from the absorber is then passed through heat-exchanger 22, inheat-exchange relation with the hot concentrated solution, and suppliedto the generator through line 34.

In the evaporator, water or some other suitable exchange medium issupplied to heat-exchanger 17, commonly referred to as the chilled watercoil, through line 35 from the individual room units and returned tosaid units through line 36. The evaporator has a refrigerant pump 37associated therewith, said pump being arranged to continuously circulateliquid refrigerant collecting in pan 19 to a spray header 39 aboveheat-exchanger 17. Under normal operation conditions, the chilled waterfrom the room units, e.g., induction of fan coil units, enters thechilled water coil 17 at approximately 54 F. and leaves through line 36at approximately 44 F.

Cooling water for the absorber and the condenser is supplied from acooling tower 40 of any conventional design, and is pumped by pump 52through lines 41 and 42 to the heat-exchanger 18 disposed in theabsorber section for removing heat generated by dilution of theconcentrated absorber solution, and then through line 43 toheat-exchanger 12 disposed in the condenser section. Heat-exchanger 12is connected by means of line 44 to a three-way valve 45 which isadapted to selectively divert water either through cooling tower 40 or abypass line 46 arranged in parallel therewith. If the minimum coolingwater temperature is called for, all of the water is diverted throughthe cooling tower, and if some higher cooling water temperature isdesired, a portion or all of the water leaving the condenserheat-exchanger 12 through line 44 may be diverted to the bypass line 46which is connected into line 42 downstream from the cooling tower.

An important aspect of the present invention concerns the control systemfor adjusting the cooling water temperature in response to varyingconditions, and particularly at system start-up and under the low loadconditions when the concentration of the absorber solution is relativelydilute. As mentioned above, if there is a fairly sudden demand forincreased capacity such that steam or hot water valve 56 (controlled inresponse to the load and commonly operated, for example, by a controlunit 54 and a bulb 55 sensing the leaving chilled water temperature inline 36 moves to a wide open position,

'3 the control system of the present invention takes remedial action toprevent violent boiling in the generator. A submaster temperatureresponsive controller 48 having bulb 49 is arranged to sense thetemperature of water flow in line 42 before it is directed into theabsorber heatexchanger 18. A master controller 50 having bulb 51responsive to the temperature of the concentrated solution leaving thegenerator through line 23 is adapted to adjust the control point atwhich the submaster controller is set. For example, at start-up or lowload, the solution concentration may be in the neighborhood of 54percent lithium bromide leaving the absorber and 58 percent leaving thegenerator and the corresponding temperature of the solution leaving thegenerator, sensed by the master controller, would be approximately 150F. A propersetting for the condenser water temperature would be 92 F. Athigh load, the solution concentrations would be approximately 59.5percent leaving the absorber and 64.5 percent leaving the generator. Thesolution temperature at the master controller would be approximately 210F. The submaster temperature would be reset for 85 F. Since thetemperature of the cooling water entering the absorber heat-exchangerbears a direct relationship with the temperature of the water enteringthe condensing coil, it is possible to locate the temperature bulb atany place in the system past the juncture of the bypass line 46 with theline 41 leading from the cooling tower.

With reference to the temperature controllers, many devices capable ofcarrying out the control requirements are available on the market.However, for the purpose of completing this disclosure, controllers 48and 50 may be of the types designated as model T-90'1 and T-900, bothmanufactured by the Johnson Service Company, Milwaukee, Wisconsin.

While this invention has been described in connection with a certainspecific embodiment thereof, it is to be understood that this is by Wayof illustration and not by way of limitation; and the scope of thisinvention is defined solely by the appended claims which should beconstrued as broadly as the prior art will permit.

What is claimed is:

1. An absorption refrigeration system comprising an evaporator, anabsorber, a generator, and a condenser connected to provide a closedrefrigeration circuit; means for conducting relatively dilute solutionfrom said absorber to said generator; means for conducting relativelyconcentrated solution from said generator to said absorber; a conduitfor supplying a heating medium to the generator in heat exchange withthe solution therein; a capacity control valve placed in said conduit,said valve being 0perated in response to the cooling load; a coolingwater circuit including a cooling tower conduit means for circulating arelatively fixed quantity of water in a closed circuit from said coolingtower to said absorber and condenser in series; means for varying thetemperature of the cooling Water in said cooling water circuit, saidmeans including first temperature control means responsive to thetemperature of cooling water entering the absorber; second temperaturecontrol means responsive to the temperature of relatively concentratedsolution conducted from said generator, said second control means actingas a master control to reset the control point of said first temperaturecontrol means such that said first temperature control means functionsas a submaster control, whereby said first and second temperaturecontrol means are operative to raise the temperature of the coolingwater supplied to the absorber and condenser as the temperature ofsolution from thegenerator drops.

2. An absorption refrigeration system comprising an evaporator, anabsorber, a generator, and a condenser connected to provide a closedrefrigeration circuit; means for conducting relatively dilute solutionfrom said absorber to said generator; means for conducting relativelyconcentrated solution from said generator to said absorber; means forcirculating water to be chilled to and from said evaporator; a conduitfor supplying a heating medium to the generator in heat exchange withthe solution therein; a capacity control valve placed in said conduit;first temperature control means for operating said capacity controlvalve in response to the temperature of chilled water leaving saidevaporator; a cooling water circuit including a cooling tower, a pumpand associated conduit means for circulating a relatively fixed quantityof water in a closed circuit from said cooling tower to said absorberand condenser in series flow, a by-pass conduit connected in parallelwith said cooling tower and a second control valve operative toselectively control the flow of cooling Water to the tower and to saidby-pass conduit to vary the temperature of the cooling water in saidcooling water circuit; a second temperature control means responsive tothe temperature of cooling water entering the absorber to operate saidsecond control valve;

system of the type including an evaporator, an absorber, a generator,and a condenser connected to provide a closed refrigeration circuit;means for-conducting relatively dilute solution from said absorber tosaid generator, means for conducting relatively concentrated solutionfrom said generator to said absorber, comprising the steps of supplyinga heating medium to the generator in heat exchange with the solutiontherein; varying the supply of said heating medium in response to thecooling load; circulating a relatively fixed quantity of cooling waterin a closed circuit to said absorber and condenser in series flow;controlling the temperature of the cooling water in said cooling watercircuit in response to the temperature of cooling water entering theabsorber to maintain'the temperature at some predetermined value;measuring the temperature of the relatively concentrated solutionconducted from said generator to obtain an approximate indication of theconcentration of said solution; and raising said predeterminedtemperature value of said cooling water as said' solution temperaturedrops.

References Cited by the Examiner UNITED STATES PATENTS 2,722,806 10/1955 Leonard 62-141 3,005,318 10/1961 Miner 62-141 ROBERT A. OLEARY,Primary Examiner.

CHARLES R. REMKE, Assistant Examiner.

3. A METHOD OF OPERATING AN ABSORPTION REFRIGERATION SYSTEM OF THE TYPEINCLUDING AN EVAPORATOR, AN ABSORBER, A GENERATOR, AND A CONDENSERCONNECTED TO PROVIDE A CLOSED REFRIGERATION CIRCUIT; MEANS FORCONDUCTING RELATIVELY DILUTE SOLUTION FROM SAID ABSORBER TO SAIDGENERATOR, MEANS FOR CONDUCTING RELATIVELY CONCENTRATED SOLUTION FROMSAID GENERATOR TO SAID ABSORBER, COMPRISING THE STEPS OF SUPPLYING AHEATING MEDIUM TO THE GENERATOR IN HEAT EXCHANGE WITH THE SOLUTIONTHEREIN; VARYING THE SUPPLY OF SAID HEATING MEDIUM IN RESPONSE TO THECOOLING LOAD; CIRCULATING A RELATIVELY FIXED QUANTITY OF COOLING WATERIN A CLOSED CIRCUIT TO SAID ABSORBER AND CONDENSER IN SERIES FLOW;CONTROLLING THE TEMPERATURE OF THE COOLING WATER IN SAID COOLING WATERCIRCUIT IN RESPONSE TO THE TEMPERATURE OF COOLING WATER ENTERING THEABSORBER TO MAINTAIN THE TEMPERATURE AT SOME PREDETERMINED VALUE;MEASURING THE TEMPERATURE OF THE RELATIVELY CONCENTRATED SOLUTIONCONDUCTED FROM SAID GENERATOR TO OBTAIN AN APPROXIMATE INDICATION OF THECONCENTRATION OF SAID SOLUTION; AND RAISING SAID PREDETERMINEDTEMPERATURE VALUE OF SAID COOLING WATER AS SAID SOLUTION TEMPERATUREDROPS.